This phrase is either the start of a very successful relationship or an indication that someone is set up to fail.
Situation 1. My brother stayed with me 6 months to help with my new son. We got a gym membership as a family as I needed yo lose 50ish pounds and he needed to lose 280ish pounds. I would get home from work ready to go workout and he would say "tomorrow" or do 10 minutes of cardio and 10 minutes of weights and be ready to go. He lost 12 pounds and gained it all back within a few weeks of returning home. I felt frustrated and sad I couldn't help him make a good and permanent change.
Situation 2. My much younger cousin stayed with me this summer and lost 30 pounds by adapting to my gym schedule and dieting though under no obligation to do so. I told her what I did and said she was an adult and could do as she wished during the summer. She lost the weight and continues to do so in a healthy manageable way upon returning to her college campus.
Situation 3. I recently had a nursery employee from my gym tell me that she wants to look like me for a wedding in 3 months. She works 2 of the 6 days I am at the gym, has free membership to said gym, and relatively few obstacles to making a change. She sees something she wants and wants a a magic recipe to make it happen without internalized change. I gave her the link to my fitness pal a week ago, she approached me again asking for me to call her when I workout to motivate her. Hmm. I don't proselytize fitness because I feel that each individual has to make that journey on their own. I feel like being nice and trying to help but would rather not be associated with someone with lower motivation than me as I tend to have sympathy workouts of lower intensity, as I discovered with my brother. I know her desires for change are a short term fix for need to look better at a wedding. Would it be rude to decline to help her any more without an explanation?

Nothing against any of your family members or friends. But I found that once I was ready to lose this weight I didn't need outside motivation from the people in my life. Having said that I love what I've found in 3fatchicks and myfitnesspal.

Over the years my friends or family would talk to me about losing weight and all I heard was blah blah blah because it meant nothing to me.

In March of this year I decided that I was tired of feeling like this and looking like this so I'm doing something about. Every person has to individually decide when they have had enough.(You probably can't tell but that is a bold period at the end of the previous sentence.)

Do what is best for you. Her fitness is not your responsibility. If she says "why didn't you call me?" say, "It never even crossed my mind." Everytime. She will get the idea if you just keep saying it.

Thanks. If I agree to help, I like to help and see progress towards a goal. It is particularly distressing to see people you really care about have setbacks or not even bother to try and make positive changes.